The British government's commitment to raise the UK greenhouse gas emission reduction target in the Climate Change Bill from 60% to 80% by 2050 is rightly ambitious. But is this yet another unrealistic green target?

The answer is yes. Many businesses, investors, green groups and policy wonks have very little confidence in the government's ability to put policies in place to meet our 2020 EU emission target, let alone an 80% reduction by 2050.

Part of the reason for this is that so many green targets have been twisted, contorted or dropped during the last 11 years. For example, there have been eight significant realignments within energy policy since 2000. The policy uncertainty created by this government dithering has resulted in too few businesses making investments in the infrastructure needed for transition to a low carbon economy. One of the most striking results of this sorry state, is the fact that this government has actually presided over rising UK emissions.

There are other problems as well. The worst kind of creative accounting has been employed for calculating this emissions target. Aviation has been excluded from the 80% target, when this is the sector expected to see by far the largest increase in emissions. It also produces emissions at high altitude which have a significantly larger impact on climate change than emissions released at sea-level.

In a recent research paper from Policy Exchange entitled, Green dreams: a decade of missed targets, we showed the extent to which the government's green targets were failing. Of 138 high-level targets set by government, 60% have been missed or were unlikely to be met. In areas such as biodiversity conservation, 88% of such targets had been missed. With a track record this poor, we should approach this week's announcement with profound skepticism.

Without a credible policy framework to drive the right investment decisions and green choices, significantly reducing UK emissions beyond that delivered by technological change, will be impossible. One of the first things any new government will have to do, is set this framework and do it both credibly and quickly.